The present invention relates to a video signal processor and a method of processing video signals.
Video signals are processed with gamma characteristics before broadcast to display apparatus having cathode ray tubes (CRT). CRT display apparatus process these video signals with reverse gamma characteristics to display images with linear gradation.
Different from CRT display apparatus, plasma display panels (PDP) and liquid crystal display (LCD) apparatus, both types having linear gradation, apply gamma correction to video signals processed with gamma characteristics to process the signals with reverse gamma characteristics for displaying images with linear gradation.
Not only achieving linear gradation, gamma correction is applied to video signals to make corrections to gamma curves constituted by input luminance signals Y-IN and output luminance signals Y-OUT in image-quality adjustments.
One example of a gamma curve for image-quality adjustments is called an S-curve such as shown in FIG. 1. D.C. components may be added (characteristics “a”) to or subtracted (characteristics “b”) from the S-curve, as shown in FIG. 2, to control brightness of black or white in gradation adjustments. The characteristics shown in FIGS. 1 and 2 may be combined, if necessary.
Japanese Unexamined Patent Publication No. 2002-27285 discloses gradation correction with no suppression of gain and gamma curve in spite of the scale of dynamic range.
In known video signal processing with gamma correction, however, a gamma curve is a predetermined fixed curve. In contrast, images carried by video signals vary with time. Thus, correction with such a fixed gamma curve cannot offer optimum image quality constantly.